The conventional cavity filter is provided with a coupling adjustment structure for adjusting the coupling frequency between the filter and the cavity, such as a resonant adjustment screw and a coupling adjustment screw. The resonant adjustment screw and the coupling adjustment screw are mostly mounted on the cover plate. In order to install the resonant adjustment screw and the coupling adjustment screw, the cover plate needs to have a certain thickness, which increases the overall size of the cavity filter. The installation of the resonant adjustment screw and the coupling adjustment screw cause the upper surface of the cover plate to be uneven, and the space of the cover plate is occupied. It is not convenient to use, and affects the appearance of the cavity filter.